Here is a forum thread on the Jellyfin forums from 2 days ago with an explanation and a solution. Looks like somehow the Roku Jellyfin client somehow has been marked as Beta which requires some extra steps for installation.

While a direct migration does not exist, since you have access to the data on both instances it would theoretically be possible to export/import the database tables from one to the other. That will require digging and knowledge on your end to figure out which data needs to move over.

Another option would be to duplicate the database from the first instance and connect to that front the second instance. From there make the changes to the second instance by hand.

Just make sure before you go mucking about with and database imports you have a good solid backup in case things go south.

Note: The above is theoretical as I have not setup am instance of Lemmy of my own. Just typical of how a database works.